The invention is based on a priority application EP 05 292 288.7 which is hereby incorporated by reference.
The invention relates to method for operating a signal lamp, in particular a railway signal lamp, wherein the signal lamp comprises as its illuminant at least one light emitting diode (=LED), and wherein the luminous intensity of the signal lamp is adapted to the brightness of the surrounding.
Such a method, and a related signal lamp arrangement, is described in US2005/0151665A1.
Railway signal lamps are used, for example, to indicate the opening status of a railway track section to a train operator. Railway signal lamps of the state of the art use power light emitting diodes (=LEDs) as its illuminant. Power LEDs have proven to be more reliable and cost-effective than conventional light bulbs.
During daytime, the light of the railway signal lamp must be bright enough for the train operator to recognize the status of the signal lamp well before arriving at the signal lamp. During nighttime, however, the luminous intensity of the signal lamp must be low enough so the train operator is not dazzled. This means that the luminous intensity of a railway signal lamp should be adapted to the brightness of the surroundings.
US2005/0151665A1 describes a signaling control device apparatus for LED traffic signalling applications. A sensor is used to determine the light load in the surroundings, and its signal is used to adapt the LED current.
The separate sensor makes the signal lamp arrangement, and in particular the electric circuit, rather complex and expensive.